College Answer

a)

Pulsus paradoxus is an exaggeration (> 12 mmHg or 10%) of the normal inspiratory decrease in systemic blood pressure.

Decreased intrathoracic pressure with inspiration results in increased venous return to right heart and bulge of IVS to left. Because the ventricle can normally also expand outward, this septal shift is usually small, and the difference in the blood pressure is therefore small between inspiration and expiration (<10 mmHg). With tamponade, the left ventricle cannot expand outward, so the septal shift is exaggerated and the difference in BP is larger. Also, the relatively higher negative pressure in the pulmonary circulation compared to the left atrium in patients with pericardial pathology pooling of blood in pulmonary veins during inspiration resulting in decreased LV stroke volume.

b)

Palpation of pulse- disappears in deep inspiration

Sphygmomanometer- Korotkoffs sounds first heard in expiration only and then in inspiration with progressive deflation

Pulse Oximeter-particularly useful in paediatrics

Arterial pressure trace- exaggerated fall of systolic pressure in inspiration

c)

Hypotension

Elevated JVP (neck vein distension with inspiration- Kussmaul’s sign) Muffled heart sounds

Tachypnoea

Exaggerated drop in diastolic CVP (Friedrich’s sign)

Absent y descent on CVP trace

Clinical signs of shock- decreased peripheral perfusion, slow capillary refill, oliguria, confusion.

d)

Tachycardia

Low QRS voltage trace Electrical alternans

Global concave ST elevation PR depression

e)

Visible pericardial effusion

Diastolic collapse of Right Atrium and Right Ventricle

Respiratory variation in left and right sided volumes. Atrial and ventricular septa move leftward during inspiration and rightward during expiration

Mitral and Tricuspid flow velocities are increased and out of phase. Mitral flow is increased on the first beat of inspiration and tricuspid flow is increased on expiration.

The IVC is distended and does not collapse on inspiration

Discussion

a) The definition of pulsus paradoxus used by the college is from Curtiss et al (1988) who demonstrated that 12 mmHg and 9% systolic variation (not 10%) are the 95% confidence limits for diagnosis of moderate or severe tamponade. Most textbooks instead use 10mmHg as a convenient round number, described by Swami and Spodick (2003) as "a quasi arbitrary but practical level".

b) there are in fact only four methods known:

• Invasive arterial pressure trace: that's the classical ICU technique of demonstrating pulsus paradoxus, and is colloquially described as a "swing" of the arterial line.
• Palpation of the radial pulse:  the disappearance of the radial pulse on inspiration was the original sign described by Kussmaul.
• Sphygmomanometry: with the blood pressure measurement cuff inflated to the level of the systolic blood pressure, one ought to hear Korotkoff sounds.  Because the systolic blood pressure falls during spontaneous inspiration, the Korotkoff sounds disappear during inspiration. 
• Pulse oximetry is "particularly useful in paediatrics" according to the college examiners; they probably said this on the basis of a study by Tamburro et al (2002). The pulse oximeter waveform does something similar to the waveform of an arterial line, i.e "a decrease in the highest value of the upper plethysmographic peak of the pulse-oximetry waveform was observed during inspiration in each patient". Tamburro et al  observed this phenomenon in eight children and adolescents, which might give rise to the impression that this technique is "particularly useful in paediatrics". This might be in reference to the practical difficulties of using invasive blood pressure monitoring in children; otherwise the technique is probably equally useful in adults. 

c) These are the clinical signs of cardiac tamponade (some available mainly via invasive monitoring waveforms)

• Nonspecific findings which include tachycardia and tachypnoea

• Beck's Triad: Muffled heart sounds, hypotension and raised CVP.
• Kussmaul's sign: the neck veins distend with inspiration, instead of collapsing. 
• Friedreich's sign: an exaggerated early drop in diastolic CVP.
• Pulsus paradoxus - an exaggeration of the normal inspiratory fall in blood pressure
• Pericardial rub  if the tamponade is associated with some sort of pericardial inflammation
• Pericardial "knock", first described by Maynard Smith  (consulting surgeon of the British Expeditionary Force, 1918)  as a sound which  "may be compared to that heard in the ear-piece of a telephone when the lever is moved up and down". 
• A third heart sound 
• Displaced apex beat 
• Characteristric CVP findings: classically, a sawtooth "M" or "W"  configuration of a raised CVP.
  
  In summary
  • The CVP is raised
  • All CVP waveform components are elevated
  • a and v waves are tall
  • x descent is steep
  • y descent is (usually) absent

d) Electrocardiograhic features of pericarditis with tamponade are:

• Tachycardia 
• Low QRS voltage trace - which develops as the result of a large volume of fluid in the way between the heart and the electodes, a fluid which has relatively poor conductivity. Not surprisingly, this feature is found more often in patients with large effusions. However,  truly humongous effusions can be present without any tamponade physiology. 
• Electrical alternans  is the presence of alternating high and low QRS complexes. LITFL has a nice example. 
• Global concave ST elevation results from the current of injury which develops from direct pressure on the myocardium. 
• PR depression - this is usually asociated with pericarditis, and because pericarditis is often associated with pericardial effusion the PR segments are often depressed in cardiac tamponade. Obviously, cardiac tamponade which is not due to pericarditis will probably have normal-looking PR segments. 
• T wave inversion may develop as a result of pericardial irritation, but is by no means unique to cardiac tamponade. 

e) Echocardiographic features listed here are from Pérez-Casares et al (2017) 

• Tachycardia is a nonspecific sign and does not merit any additional discussion
• Low QRS voltage trace - which develops as the result of a large volume of fluid in the way between the heart and the electodes, a fluid which has relatively poor conductivity. Not surprisingly, this feature is found more often in patients with large effusions. However, you do not have to have a large effusion to develop cardiac tamponade (less than 200ml could be fatal if i develops rapidly). Conversely, truly humongous effusions can be present without any tamponade physiology. Ergo, low QRS voltage is a sign with poor sensitivity. Eisenberg found it to have a sensitivity of just 25% for cardiac tamponade.
• Electrical alternans  is the presence of alternating high and low QRS complexes. LITFL has a nice example. It is usually associated with massive pericardial effusion, and is caused by the mechanical movement of the contracting heart, which is rhythmic and which changes its position within the dilated pericardial sack relative to the ECG electrodes. Alternans is merely the alternating high-low pattern of QRS complexes; there is also the phenomenon known as total alternans, where the QRS complexes are opposite (i.e. alternating up and down).  Therefore, it is associated with cardiac tamponade only insofar as massive effusion is associated with tamponade. Small effusions or the relatively immobile blood clot following cardiac surgery will not produce this effect. 
• Global concave ST elevation results from the current of injury which develops from direct pressure on the myocardium. It is rarely greater than 5mm. Badiger et al (2012) describes this very well, and offers discriminating features which help to distinguish it from myocardial infarction.
• PR depression - this is usually asociated with pericarditis, and because pericarditis is often associated with pericardial effusion the PR segments are often depressed in cardiac tamponade. Obviously, cardiac tamponade which is not due to pericarditis will probably have normal-looking PR segments. Eisenberg found that PR segments were unremarkable in more than half of all tamponade cases.  
• T wave inversion may develop as a result of pericardial irritation, but is by no means unique to cardiac tamponade. Pericarditis produces these changes, and they tend to resolve as the condition improves.